1. Field of the Invention
The present invention relates to a method for producing a conductive oxide-deposited substrate and a conductive oxide-deposited substrate which is used for producing functional devices such as displays, image sensors, solar batteries and illuminations using solid light sources.
The present invention also relates to a method for producing a MIS laminated structure which is a basic structure of a switching element which controls charge transfer in connection with a light receiving and emitting element and a memory element, and a MIS laminated structure.
2. Description of the Related Art
Conventionally, a conductive oxide-deposited substrate represented by In2O3—SnO2 (ITO: Indium-Tin-Oxides) which is processed in a wiring shape is used in displays, image sensors or the like. In devices having functional surfaces such as solar batteries and illumination using solid light sources, a conductive oxide-deposited substrate in which a conductive oxide is processed into a concavo-convex shape is used for the purpose of enhancing efficiency of current collection or taking in and removing light. The conductive oxide is generally processed by a method of processing the conductive oxide by photolithography using a photomask.
For example, Japanese Patent Application Laid-Open (JP-A) No. 2006-066362 discloses a method for producing an ITO film including a step of forming a pattern in the ITO film which includes a step of forming a photoresist layer, in which a pattern is formed, on the ITO film, a step of removing a part of the ITO film using the photoresist layer, and a step of removing the photoresist layer.
JP-A No. 2006-114428 discloses that an ITO film is ablated by a laser beam, which is photolytic reaction, and the ITO film is selectively irradiated with a laser beam so as to remove an irradiated area of the ITO film, thereby forming a removed pattern in the ITO film.
Japanese Patent (JP-B) No. 3229610 discloses a method for producing an ITO electrode, wherein an ITO film having a resistance of 1×10−3Ω·cm or more is deposited and etched in a given pattern, a film needs to be heated is deposited, and then the film and the ITO film are simultaneously heated in a clean oven so as to decrease the resistance of the ITO film to less than 1×10−3Ω·cm, thereby producing an ITO electrode.
In JP-A No. 2006-004594, the inventors of the present invention propose a method of forming a fine structure, including at least a step of irradiating a medium with light, and a step of etching the medium, wherein the medium has a laminated structure consisting of a light absorption layer and a thermal reactive layer.
However, these related arts do not disclose the invention of directly processing and forming a conductive part into a pattern using light.
To a light receiving and emitting element, a switching element consisting of a thin film transistor and the like is connected to control charge transfer. Recently, as a semiconductor material for such switching element, a development of a technology using an organic semiconductor is outstandingly progressed. That is, by the use of an organic semiconductor as a semiconductor material of the switching element, a low temperature wet process such as an inkjet printing process, spin coating process and printing process can be employed upon production of an element. As a result, the cost of the process can be decreased, a substrate can be formed of a plastic, and moreover a flexible device can be expected.
On the other hand, the semiconductor property of an organic semiconductor material such as charge transfer degree has not been satisfied, as it now stands. For example, as disclosed in “Nature, Vol. 432 (2004) 488” and JP-A No. 2007-194628, an inorganic semiconductor material capable of being formed by a low temperature process is vigorously developed.
Examples of methods for producing a switching element, in which an inorganic semiconductor material is formed into a semiconductor layer, include a method for patterning each layer using both wet etching treatment and dry etching treatment as disclosed in JP-A No. 2002-116714, and a method for producing a switching element only by a wet etching treatment as disclosed in JP-A No. 2007-123700.
Any methods described above require a step of forming a resist mask by photolithography.
A method for producing a thin film transistor by a conventional photolithography and etching treatment is shown in FIGS. 1A to 1D. FIGS. 1A to 1E are cross sectional views of an example of a structure of a top-gate thin film transistor.
FIG. 1A shows a photolithography process of a semiconductor thin film performed in an arrow direction. A photoresist 6 is coated on a semiconductor thin film 5 and patterned by photolithography 7, the patterned photoresist 6 is covered with an etching mask 8, and then the semiconductor thin film is processed.
FIG. 1B shows a photolithography process of source and drain electrodes performed in an arrow direction. 9 denotes a source and drain electrode thin film, 10 denotes a photoresist, and 11 denotes photolithography.
FIG. 1C shows a photolithography process of a gate insulating film performed in an arrow direction, 12 denotes a gate insulating film, 13 denotes a photoresist and 14 denotes photolithography.
FIG. 1D shows a photolithography process of a gate electrode performed in an arrow direction. 15 denotes a gate electrode thin film, 16 denotes a photoresist and 17 denotes photolithography. FIG. 1E shows an example of a basic structure of a thin film transistor, in which 18 denotes a substrate, 19 denotes a semiconductor thin film, 20 denotes a gate insulating film, 21 denotes a source electrode, 22 denotes a drain electrode and 23 denotes a gate electrode.
The conventional methods need four photolithography processes, when a basic structure of a thin film transistor as shown in FIG. 1E is produced. The process cost increases according to the number of photomasks and processes. Therefore, the issue of device cost reduction is solved by decrease of the number of photolithography processes. Additionally, there is an issue how to avoid plasma damage on a resin substrate material when an inorganic semiconductor material on a plastic substrate is processed by a dry etching method.